DESCRIPTION: This is a study of genetic and environmental determinants of venous thromboembolism (VTE) in the Rochester Minnesota Olmsted County population. The specific aims of the study are: 1) to update the 1966-95 inception cohort to include Olmsted County residents with VTE during the five year period, 1996-2000; 2) to extend the analysis of risk factors for VTE by identifying two Olmsted County residents (controls) without VTE matched by age and gender to each definite or probable case within the 1996-2000 cohort, and to obtain plasma and genomic DNA from all cases and controls and perform a case-control study to test the hypothesis that first specific diseases are related to VTE and mutations of the factor five and prothrombin are independent risk factors for VTE in the community; and interactions between environmental and genetic factors. They will determine the population attributable risk for VTE associated with each risk factor, both individually and collectively for all significant risk factors. They will then compare two Olmsted County residents who received major surgery without developing VTE matched by date and type of surgery to a case with VTE within three months after surgery in order to look at risk factors related to surgery and genetic markers. They will do a similar analysis this time using two Olmsted County residents who were hospitalized for medical illness without developing VTE matched by gender and date of hospitalization to a case who developed VTE within three months after hospitalization and perform a case-control study to test the hypothesis again that risk factors and genetic markers are associated with elevation of risk of VTE. Finally, the investigators will plan to extend their analysis of current VTE in relationship to use of standard heparin and low molecular weight heparin.